1. Technical Field
The present disclosure relates to a digital-to-analog converter using capacitors and an operational amplifier and, more particularly, to a digital-to-analog converter that can be highly integrated due to its small area and that can rapidly perform a stable converting operation.
2. Discussion of the Related Art
A digital-to-analog converter that converts digital data into an analog signal includes a resistor string converter and a decoder and a capacitor converter using the charging of a capacitor and charge distribution.
FIG. 1 is a block diagram of a conventional resistor string converter. Referring to FIG. 1, the resistor string converter includes a resistor string 102, a decoder 104 and a buffer 106. When a maximum voltage Vmax and a minimum voltage Vmin are applied to both ends of the resistor string 102, a plurality of voltages Vi1, Vi2, . . . , Vik falling between the maximum voltage Vmax and the minimum voltage Vmin are applied to the decoder 104. The decoder 104 receives a digital data input, selects from among the voltages Vo1, Vo2, . . . , Vok corresponding to the received digital data, and outputs the selected voltages Vo1, Vo2, . . . , Vok through output terminals. The selected voltages Vo1, Vo2, . . . , Vok output through the output terminals are supplied to an external device (not shown) through the buffer 106.
The aforementioned resistor string converter performs a stable digital-to-analog converting operation. This resistor string converter, however, requires a large area and, thus, is not suitable for a high level of integration.
The area of the conventional resistor string converter illustrated in FIG. 1 is increased 2N times when the number of bits of input data is increased by N. For example, when the size of a decoder of a 6-bit system is 100, the size of a decoder of an 8-bit system becomes 400 (=100×22) and the size of a decoder of a 10-bit system becomes 1600 (=100×24). Accordingly, it is difficult to use the resistor string converter in systems processing more than 10 bits.
To solve this problem, digital-to-analog converters suitable for a high level of integration have been studied in various ways. One of the digital-to-analog converters suitable for a high level of integration is a digital-to-analog converter using the charging of a capacitor and a charge distribution.
FIG. 2 is a circuit diagram of a conventional capacitor converter using the charging of capacitors and a charge distribution. Referring to FIG. 2, the capacitor converter includes a digital data input unit 202 having data switches Sd1 and Sd2, a charging switch Sc1, a charging capacitor C1, a distribution switch Sc2, a distribution capacitor C2, and an initialization switch Sc3. The initialization switch Sc3 discharges the charging capacitor C1 and the distribution capacitor C2 to initialize them before a converting operation.
When the data switches Sd1 and Sd2 transfer the upper limit voltage Va or the lower limit voltage Vb in response to the logic level of the first bit of the digital data input to the data input unit 202, the charging switch Sc1 is closed and subsequently opened such that the charging capacitor C1 is charged with the upper limit voltage Va or the lower limit voltage Vb. Then the distribution switch Sc2 is closed and subsequently opened to distribute the charges stored in the charging capacitor C1 to the distribution capacitor C2. Subsequently, the charging capacitor C1 is charged with the upper limit voltage Va or the lower limit voltage Vb in response to the logic level of the second bit of the input digital data and the charges of the charging capacitor C1 are distributed to the distribution capacitor C2 such that charges are accumulatively stored in the distribution capacitor C2.
The aforementioned operation is repeated n times in the case of n-bit data to finally charge the distribution capacitor C2 with the voltage Vo corresponding to the input digital data.
The converting operation using the charging capacitor C1 and the distribution capacitor C2, however, requires a long period of time for generating a final voltage, because it has to perform n charging and distribution operations to convert n-bit data into an analog signal. Furthermore, the operation of the capacitor converter is not stable and, thus, the reliability of the capacitor converter is deteriorated even though the area of the capacitor converter is reduced.